THE OLD WORLD MONKEYS
The Sylvian fissure (L.S.) begins in a vallecula on the inferior surface of the brain. It passes upwards and backwards to end in the parallel sulcus (P.S,). The latter is arched over by the diverging limbs of a Y-shaped
FIG. 12. — The brains of the lower Primates. The left-hand figures are the outer surfaces of the hemispheres, and the right-hand figures are the mesial surfaces. A. A', Lemur macaco; B.B', PerodicticiLS potto; C.C', Cebus fatuelhis : D.D', ^lacacus nemestrinus. Letters explained in text.
system of sulci formed by the intraparietal (I-P.S.) and simian (S.S.) sulci. The inferior occipital (I.O.S.) and lateral occipital (L.O.S.) sulci are well marked.
The insula or island of Eeil is concealed posteriorly, but anteriorly it passes forwards to the fronto-orbital